The 1028 is the shelter carrier version of this truck and would most likely have had an S250 shelter mounted in the back. Beyond that it could have had almost anything inside. The common rigs were RTTY (radio teletype) rigs for long range HF communications. Early RTTY shelters were the AN/GRC-46 that were replaced by the AN/GRC-142/144 systems.
Beyond that these same shelters were used for VHF comm systems, UHF aircraft control systems, SATCOM systems, tactical jammers, tropo scatter systems, the list goes on and on.
A "working commo" truck will require you to have an amateur radio license for anything beyond a CB or FRS/MRS system so keep that in mind if you intend to transmit. Monitoring (listening) is still free unless someone plants a bug up the FCCs behind and they outlaw it.
Have fun, it's a great hobby
Kurt KG6KMJ